If long exposure astrophotography is carried out with a fixed photographing apparatus, the movement path of the celestial objects during a long exposure form straight or curved light trails in the captured image because celestial objects move relative to the photographing apparatus due to the earth's rotation (diurnal motion).
To carry out a long exposure in order to photograph a celestial object(s) so that the celestial object appears to be still (a luminous point), an equatorial equipped with an auto tracking system is generally used to photograph the celestial object(s) while moving the photographing apparatus relative to the celestial object(s).
However, an equatorial equipped with an auto tracking system is generally expensive, heavy and difficult to handle; in addition, it is essential to carry out a polar alignment procedure in which the polar axis of the equatorial is brought into alignment with the north celestial pole.
In recent years, a method has been proposed in which a fixed photographing apparatus performs a plurality of continuous photographing operations (exposure operations) without using an equatorial, the amount of shift of the plurality of photographed images are thereafter detected, and a single image is obtained by superimposing each photographing image (Patent Literature 1 and 2).
However, in this method, it is practically impossible to correctly calculate the shift amounts of the plurality of photographed images. Furthermore, in a photograph of a celestial object(s) as a collective image of a plurality of celestial object(s), it is extremely difficult to recognize the same celestial object without error. Furthermore, since the movement (diurnal motion) of the celestial object(s) during astrophotography is very slow, if the period (photographing interval) for carrying out a plurality of photographing operations is too short, the plurality of photographing images become the same from a macro viewpoint (a large number of similar photographing images are obtained), so that the burden on the CPU increases due to unnecessary arithmetic processes being carried out thereby.
Whereas, auto-tracking astrophotography has been proposed in which a photographing operation is carried out while driving (moving) an image sensor of a photographing apparatus, with the photographing apparatus remaining fixed, without using an equatorial (Patent Literature 3 and 4).
However, in this method, an actuator for precisely moving the image sensor is necessary, and the production and control of such an actuator is difficult.